Patients with intractable partial epilepsies who may benefit from surgical treatment are studied for purposes of localization of a single seizure focus by means of arrays of stereotactically implanted intracerebral electrodes, long term telemetric EEG monitoring and simultaneous videotape recordings of all behavioral manifestations. Certain patterns of ictal EEG onset have been found to have predictive value of surgical success in retrospective studies of 2-15 years follow up. Correlations with frequency of interictal spiking at significant sites to yield the same information are being carried out. The possibility of computer detection from surface recordings with simultaneous depth recordings in the temporal lobe is under study. Different stages of epileptogenesis of neurons in deep temporal lobe have been studied with fine wire microelectrodes. The interictal firing patterns of single neurons ipsilateral to the focus often exhibited bursts when contralateral neurons did not. Sharp EEG waves were almost always associated with action potentials from nearby neurons. During clinical seizures firing rates of neurons near the focus increased during the small amplitude high-frequency EEG phase and decreased during the high amplitude EEg phase. In patients with verbal learning problems selective loss of verbal information occurs in the process of storage and transfer of such information rather than during the initial encoding event. The total amount of spiking activity recorded from depth electrodes was related negatively with intelligence and the degree of lateralization of the spike activity was related positively with memory functioning and a psychosocial rating of the degree of independence. Progressive loss of dendritic spines and axonal degeneration of great severity have been found in epileptogenic cortical regions studied by Golgi preparations and electron microscopy. BIBLIOGRAPHIC REFERENCES: Babb,T.L., Mariani,E., Strain,G.M., Lieb,J.P., Soper,H.V. and Crandall,P.H. A sample and hold amplifier for stimulus artifact suppression. Submitted to Electroenceph. clin. Neurophysiol. 1977. Halgren,E., Babb,T.L. and Crandall,P.H. Post-EEG seizure depression of human limbic neurons is not determined by their response to probable hypoxia. Epilepsia 18 (1977) 89-93.